1. Field of the Invention
The present invention relates to laser light scanning systems which “read” or “write” indicia, for example, bar code symbols, having parts with different light reflectivities, and, in particular, to control circuitry which enables a single scanning system to adaptively alter a light beam pattern in response to control signals to perform either a “read” or “write” operation.
2. Description of the Related Art
Various optical readers and optical scanning systems have been developed heretofore for reading bar code symbols appearing on a label, or on the surface of an article. The bar code symbol itself is a coded pattern of indicia comprised of a series of bars of various widths spaced apart from one another to bound spaces of various widths, the bars and spaces having different light-reflecting characteristics. The readers and scanning systems electro-optically transform the graphic indicia into electrical signals which are decoded into alphanumerical characters. The resulting characters are descriptive of the article and/or some characteristic of the article to which the symbol is attached. Such characters are typically an input data to a data processing system for applications in point-of-sale processing, inventory control, and the like.
As used in this specification and in the following claims, the terms “symbol”, “bar code,” and “bar code symbol,” are used to denote a pattern of variable-width bars separated by variable-width spaces. The foregoing terms are intended to be broadly construed to cover many specific forms of one- and two-dimensional patterns including alpha-numeric characters, as well as, bars and spaces.
The specific arrangement of bars or elements in a symbol defines the character represented according to a set of rules and definitions specified by the code. This is called the “symbology” of the code. The relative size of the bars and spaces is determined by the type of code used, as is the actual size of the bars and spaces. The number of characters per inch represented by the barcode symbol is referred to as the density of the symbol.
To encode a desired sequence of characters, a collection of element arrangements are concatenated together to form the complete symbol, with each character being represented by its own corresponding group of elements. In some symbologies, a unique “start” and “stop” character is used to indicate where the barcode symbol begins and ends. A number of different barcode symbologies presently exist. These symbologies include one-dimensional codes such as UPC/EAN, Code 39, Code 128, Codabar, and Interleaved 2 of 5.
In order to increase the amount of data that can be represented or stored on a given amount of symbol surface area, several new symbologies have been developed. One new code standard, Code 49, introduced a two-dimensional concept of stacking rows of characters vertically instead of extending symbols bars horizontally. That is, there are several rows of bar and space patterns, instead of one long row. The structure of Code 49 is described in U.S. Pat. No. 4,794,239. Another two-dimensional code structure known as PDF417 is described in published European Patent Application Serial No. 90119399.5, commonly assigned to the assignee of the present invention, and hereby incorporated by reference.
Scanning systems for reading bar codes have been disclosed, for example, in U.S. Pat. Nos. 4,251,798; 4,369,361; 4,387,297; 4,409,470; 4,760,248; 4,896,026, all of which have been assigned to the present invention. As disclosed in some of the above patents, and particularly in U.S. Pat. No. 4,409,470, one existing scanning systems comprises a hand-held, portable laser scanning head. The hand-held scanning system is configured to allow a user to manually aim a light beam emanating from the head at a target symbol.
These scanning systems generally include a light source consisting of a gas laser or semiconductor laser. The use of semiconductor devices as the light source in scanning systems is especially desirable because of their small size, low cost and low power requirements. The laser beam is optically modified, typically by a focusing optical assembly, to form a beam spot having a certain size at a predetermined target location. Preferably, the cross section of the beam spot at the target location approximates the minimum width between symbol regions of different light reflectivity, i.e., the bars and spaces.
In the conventional scanning systems, the light beam is directed by lens or similar optical components along a light path toward a target symbol. The scanner operates by repetitively scanning the light beam in a line or a series of lines across the target symbol by movement of a scanning component such as a mirror disposed in the path of the light beam. The scanning component may sweep the beam spot across the symbol, trace a scan line across and beyond the boundaries of the symbol, and/or scan a predetermined field of view.
Scanning systems also include a sensor or photodetector which functions to detect light reflected or scattered form the symbol The photodetector or sensor is positioned in the scanner in an optical path so that it has a field of view which extends at least across and slightly beyond the boundaries of the symbol. A portion of the light beam reflected from the symbol is detected and converted into an analog electrical signal.
The analog electrical signal produced by the photodetector is converted by a digitizer circuit in the scanner into a pulse-width modulated digital signal having widths corresponding to the physical widths of the symbol elements.
The pulse-width modulated digitizer signal from the digitizer is decoded, based upon the specific symbology used for the symbol, into a binary data representation of the data encoded in the symbol. The binary data may then be subsequently decoded into the alphanumeric characters represented by the symbol.
The decoding process in conventional scanning systems usually works in the following way. The decoder receives the pulse-width modulated digital signal from the scanner, and an algorithm implemented in software attempts to decode the scan. If the start and stop characters and the characters between them are successfully and completely decoded, the decoding process terminates and an indicator (such as a green light and/or an audible beep) is initiated to inform the user. Otherwise, the decoder receives a next scan, attempts another decode on the scan, and so on, until a completely decoded scan is achieved or no more scans are available.
Scanning systems for writing or printing indicia have been disclosed, for example, in U.S. Pat. Nos. 4,085,423 and 4,908,813. The use of thermally sensitive paper, or utilizing dyes which are sensitive to radiation in a particular frequency spectrum, is known for use in printing systems, such as exemplified in U.S. Pat. No. 5,014,072.
Prior to the present invention, there has not been a single apparatus which is designed to perform both reading and writing on the same document or medium.